Sense amplifier including multiple conduction state field effect transistor

Abstract

An integrated circuit is provided which includes a sensing circuit. In the sensing circuit, a pair of conductors including a first conductor and a second conductor are adapted to conduct a first differential signal having a small voltage difference and a second differential signal having a rail-to-rail voltage difference. A sense amplifier is coupled to the pair of conductors, the sense amplifier being operable to amplify the first differential signal into the second differential signal. The sensing circuit further includes a multiple conduction state field effect transistor or “multi-state FET” which has a source, a drain, and a gate operable to control conduction between the source and the drain. The multi-state FET has a first threshold voltage and a second threshold voltage which is effective at the same time as the first threshold voltage such that the multi-state FET is operable by the gate voltage to switch between an essentially nonconductive state, a first conductive state when a gate-source voltage applied between a gate and a source of the FET is between the first threshold voltage and the second threshold voltage, and a second conductive state when the gate voltage exceeds the second threshold voltage. The multi-state FET is used to perform an operation included in amplifying the first signal into the second signal by the sense amplifier.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to integrated circuits which include sense amplifiers such as used to amplify a small voltage swing signal into a rail-to-rail voltage swing signal.[0002]Frequently, small voltage swing signals need to be amplified into rail-to-rail voltage swing signals when converting analog signals into digital signals as well as when restoring a weak signal used in a digital system to full digital logic levels. A particular type of circuit used to perform such function in a dynamic random access memory (“DRAM”) is known as a sense amplifier. Sense amplifiers are used in both dedicated stand-alone DRAM chips, as well as chips which include an embedded DRAM as a functional element of the chip. Sense amplifiers typically operate by converting a signal representing a charge stored on a storage capacitor of a memory into a rail-to-rail voltage signal.[0003]FIG. 1 is a circuit-level diagram illustrating a sense amplifier 1 according to the...

AI Technical Summary

Benefits of technology

[0011]According to an aspect of the invention, an integrated circuit is provided which includes a circuit for amplifying a small voltage swing signal into a second signal having a rail-to-rail voltage swing. Such circuit includes a conductor adapted to conduct a first signal having a small voltage swing and a second signal having a rail-to-rail voltage swing; and an amplifier coupled to the conductor which is operable to amplify the first differential signal into the second differential signal. The amplifier include a multiple conduction state field effect transistor (“multi-state FET”) having a source, a drain, and a gate operable to control conduction between the source and the drain. The multi-state FET has a first threshold voltage and a second threshold voltage effective at the same time as the first threshold voltage, and the gate is operable to control the multi-state FET between multiple operational states which include a) an essentially nonconductive state when a gate-source voltage applied between the gate and the source does not exceed the first threshold voltage and does not exceed the second threshold voltage and in which a source-drain current between the source and the drain is at most negligible; b) a first conductive state when the gate-source voltage exceeds the first threshold voltage and does not exceed the second threshold voltage, such that the source-drain current has a first operating value; and c) a second conductive state when the gate-source voltage exceeds the first threshold voltage and the second threshold voltage such that the source-drain current has a second operating value at least about ten times larger than the first operating current value; wherein the multi-state FET is operable by the gate-source voltage to switch between the essentially nonconductive state, the first conductive state and the second conductive state to perform an operation included in amplifying the first signal into the second signal by the amplifier.

[0012]According to anothe

Problems solved by technology

One problem with the above-described circuitry is the large area required by the sequential pull-down circuit 2.

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